Object centering and moving mechanisms have previously been proposed. In U.S. Pat. No. 3,504,719, a lifting and centering device for variable diameter logs is disclosed with each end of the log raised by a fluid cylinder until two sensing arms at each end are actuated in sensing the diameter and actuate a switch at each end of the log to discontinue movement of the respective fluid cylinder. A somewhat similar arrangement is disclosed in U.S. Pat. No. 4,116,094 for centering the position of two railroad car wheels on a single axle. Each wheel is lifted independently by separate motors and when the diameter is sensed, the particular motor is de-energized to thus center each end of the axle.
In U.S. Pat. No. 3,791,564, a longitudinally moving pipe is centered, even though the pipe may have enlarged portions, by means of an upper V-roller on one vertical run of an endless chain and a lower V-roller on the opposite run of that endless chain.
Multiple spindle automatic machine tools are those machine tools which are used for repetitive machining of identical workpieces where a large volume of workpieces is desired. Typically, such machines are used to produce millions of identical parts. Such machines are expensive, but when properly set up to machine a particular workpiece, the machines operate with a bare minimum of attention from an operator, and hence, the manufacturing cost per piece is at a minimum. Such machines operate on a range of sizes of chucked workpieces, or, where used with long bar stock, with a range of diameters of such bar stock, either round or polygonal in cross section. Where such machines are present but not in use in production, this is a large capital investment remaining idle, so it is highly desirable to be able to put the machine to use, even if it is for a relatively short run. However, many such multiple spindle automatic machine tools require eight hours or more for set-up time to change all the tooling and make all the adjustments necessary for a new size of bar stock and a new and different piece to be produced. Just to change the size of the bar stock, in the prior art machines, one must change the escapement mechanism to feed a different size bar into the bar feeder and also one must change the adjustment to support the bar on the same center line as the spindle of the machine tool. On the usual prior art machines, this is accomplished by replacing several semicylindrical spacers inside a longitudinally split tube. This is lost production time for the installation and adjustment, and additional cost results from the manufacture and storage of such spacers.
The prior art constructions have the deficiency of being able to lift the object only a minor fraction of the diameter of such object and, hence, are not suitable for mechanisms wherein a large lifting distance is required.
Accordingly, the problem to be solved is how to construct a machine tool which will lift and center objects, such as elongated bars for a machine tool, so that the bars are on the center line of the machine tool spindle regardless of the diameter of such bars and regardless of the distance to be lifted.